Checking and fault-indicating arrangements

ABSTRACT

A checking and fault-indicating arrangement is provided for four or a larger even number of processors in a data processing system. During a first predetermined period, odd-numbered processors perform a processing operation and the input date applied to one of the odd-numbered processors is also applied to a particular one of the adjacent even-numbered processors and the output of the two processors is compared in a comparator which provides a significant output if one of the processors are faulty. During a second predetermined period, even-numbered processors perform a processing operation and the input data applied to the other adjacent one of the even-numbered processors is also applied to said one odd-numbered processor and the output of the two processors is compared in a second comparator which also provides a significant output if one of the processors is faulty. The significant outputs of the two comparators are applied to an indicating arrangement which indicates the faulty processor.

United States Patent 72] Inventors Alexander Schroder Philip;

John Richard Francis, both of Liverpool, England [21] Appl. No. 11,760 [22] Filed Feb. 16, 1970 [451 Patented Nov. 30, 1971 [731 Assignee Automatic Telephone 8: Electric Company Limited Liverpool, England [32] Priority Feb. 17, 1969 [33] Great Britain (31 8,472/69 [541 CHECKING AND FAULT-INDICATING ARRANGEMENTS 6 Claims, 2 Drawing Figs.

[52] US. Cl 235/153, 340/1461, 340/1725, 340/149 [51] Int. Cl ..G06l11/08, (306i 1 1/04,G06f1 1/00 150] FieldolSearch 235/153; 340/1461, 1725.149

[56] References Cited UNITED STATES PATENTS 3,409,879 11/1968 Keister 340/1725 Primary ExaminerMalcolm A. Morrison Assistant Examiner-James F. Gottman Arlorney Young 8: Thompson ABSTRACT: A checking and fault-indicating arrangement is provided for four or a larger even number of processors in a data processing system. During a first predetermined period, odd-numbered processors perform a processing operation and the input date applied to one of the odd-numbered processors is also applied to a particular one of the adjacent evenmumbered processors and the output of the two processors is com pared in a comparator which provides a significant output if one of the processors are faulty. During a second predetermined period, even-numbered processors perform a processing operation and the input data applied to the other adjacent one of the even-numbered processors is also applied to said one odd-numbered processor and the output of the two processors is compared in a second comparator which also provides a significant output if one of the processors is faulty, The significant outputs of the two comparators are applied to an indicating arrangement which indicates the faulty proces- ICOHPl/ZI CHECKING AND FAULT-INDICATING ARRANGEMENTS The present invention relates to checking and fault-indicating arrangements in particular to arrangements for checking the functioning of arrangements for processing data and also for indicating the identity of any processing arrangement of a plurality of processing arrangements that is malfunctioning if such a condition should manifest itself in any of the processing arrangements.

A disadvantage in the provision of checking and fault-indication arrangements for processing arrangements of the type mentioned is that hitherto rather a large amount of logic circuitry has been required for this purpose.

it is therefore an object of this invention to overcome the beforementioned disadvantage in a simple and inexpensive manner.

According to the invention, in a checking and fault-indicating arrangement associated with an even number of processors, at least four in a data processing arrangement. the processors are formed into two equal groups and during a first predetermined period the processors of the first group each perform a processing operation and the data applied for processing to a processor of the first group is also applied to a particular processor of the second group while during a second predetermined period the processors of the second group each perform a processing operation and the data applied for processing to another processor of the second group is also applied to said processor of the first group and the outputs of said processor of the first group and said particular processor of the second group are each fed to a first comparator individual to the two processors whereas the outputs of said other processor of the second group and said processor of the first group are each fed to a second comparator individual to the two processors whereby if said processor of the first group is faulty the outputs of said processor of the first group and said particular processor of the second group will differ and a significant output will be obtained from said first comparator during said first period and the outputs of said other processor of the second group and said processor of the first group will differ and significant output will be obtained from said second comparator during said second period, the faulty processor being identified by an indicating arrangement to which the significant outputs of the two comparators are applied.

The invention will be better understood from the following description of one embodiment read in conjunction with the accompanying drawings comprising FIGS. 1 and 2 which illustrate a logic circuit diagram incorporating processing arrangements for processing data to and from register stores and also incorporates logic circuitry in accordance with the present invention.

Before embarking upon a description of the circuit diagram illustrated in FIG. 1 and FIG. 2, which should be placed sideby-side with FIG. I to the left of FIG. 2, consideration will first be given to the symbols shown therein. Referring then to the rectangular blocks designated REGI, REG2, REG3 REGN, these represent a plurality of multistage shift registers of known type, each register employing a suitable bistable device in each stage. The rectangular blocks designated PROC], PROCZ, PROC3 PROCN represent a plurality of processors each of which is provided with the necessary logic circuitry for handling input data and processing the input data to and from its associated shift register. Further the rectangular blocks designated COMPl/Z, COMP2/3, COMP3/4 COMPN/l represent comparator circuits of the nonequivalence type with perform an EXCLUSIVE-R func tion, in which a significant output is only forthcoming at the output of the circuit when there is a significant signal present on either one or other of its two inputs. In the circuit illustrated, each comparator compares the outputs of adjacent processors and only produces a significant output when these outputs are at variance.

The remaining rectangular boxes designated Tl/2. T2/3, T314 TN]! and Tl, T2, T3 TN, and which are divided into two portions designated 5 and R, represent bistable devices typically comprising a pair of cross-coupled transistors. As is well known, the bistable device has two stable states and in the circuit diagram, for each bistable device, these two states are represented by the symbol S for the socalled set" state and the symbol R for the so-called "reset state. In operation, taking any bistable as an example, if the bistable is considered to be in its reset" state, a significant output will be present at the output (the outputs are located on the lower part of the symbol) of the reset" R side of the bistable only. If now a significant signal is applied to the input (the inputs are located on the upper part of the symbols) of the set" 5 side of the bistable, a transposition of states will occur and a significant output signal will now appear at the output of the set S side of the bistable only. To cause a further transposition of states to the reset R state a significant signal is applied to the input of the "reset R side of the bistable whereupon the bistable becomes transposed and a sig nificant output signal appears at the "reset R side of the bistable only. in the circuit illustrated in the diagram. only the set outputs of the bistables are utilized.

The remaining symbols, comprising a circle enclosing the numeral 2 and each having two inputs, shown by the arrowed leads, and a single output, shown by the lead without the arrow, represent gate circuits of the type which perform an AND function, ie only when significant signals occur concur rently on the two inputs does a significant signal occur at the output. These gate circuits are typically of the diode/resistor type.

it will be noted that of the plurality of arrangements ofN registers and their associated processors and circuitry only four such arrangements are shown and these are those comprising register REGl with processor PROCl, register REGZ with processor PROC2, register REG3 with processor PROC3 and register REGN with processor PROCN. Register REG4 with processor PROC4 to register REG(N-l with processor PROC(N-l) are not shown for the sake of simplicity, but it should be appreciated that these registers and processors are connected in a manner similar to the corresponding registers and processors which are shown. Similarly with regard to the circuitry concerned with fault indication and identification only comparators COMPl/Z, COMP2/3, COMP3/4, and COMPN/l and associated bistable devices Tl/2, T2/3, T3/4 and TN/l respectively and T1, T2, T3 and TN respectively in addition to gates GFl, GF2, GF3 and GFN respectively are shown. Comparators COMPd/S to COMP(N1 )IN and their associated bistable devices T4/5 to T(N-l)/N respectively and T4 to T(Nl) respectively in addition to gates GF4 to OH N-l) respectively are not shown for the sake of simplicity but it should be understood that these bistable devices and gates are connected in a manner similar to the corresponding bistable devices and gates which are shown.

The arrangement of the complete circuit is such that the individual similar portions of circuitry, for instance each proces sor with its associated register and logic circuitry such as processor PROCI and register REG! together with gates GlA, GlB GIG, and each fault-indication and identification circuits such as that comprising comparator COMPl/Z, bistable Tl/2, gate SH and bistable T1, are interconnected in such a manner that a so-called ring is formed, with the individual circuits in the ring" which are nominated as the first individual circuits, being connected to the respective second individual circuits and these being so connected to the respective third individual circuits and so on through the other individual circuits to the respective last individual circuits which are connected to the respective first individual circuits, the rotation being taken in a clockwise direction.

Dealing with these interconnections in ore detail, firstly attention is drawn to the interconnections between the output of each register and the input of its immediately preceding processor. These interconnections arrange for the output data from each register to be passed to the input of the immediately preceding processor in one of two specific periods or phases upon the closure of the appropriate gate circuits (appropriate ones of gates 61A, 02A, 63A GNA) for processor arrange ment checking purposes. To effect these two specific periods or phases, two separate successive pulses of equal duration and designated TM] and TMZ are provided. In the first period, pulse TMl is used, amongst other things, to gate the output data from each odd register to the input of an even processor whereas in the second period, pulse TMZ is used, amongst other things, to gate the output data from each even register to the input of an odd processor.

Secondly, attention is drawn to the interconnections between adjacent fault indication and location circuits. These extend from the "set" S output of the bistable, on the output of the comparator of one individual circuit, to an input of an AND gate in the succeeding individual circuit. For instance from the set" S side of bistable TI/2 connection is made to an input of ate GFZ; the output of the "set" S side of bistable T2/3 is connected to an input of gate GF3 and so on in similar manner between the succeeding individual circuits until finally the output of the "set" S side of bistable TN/l is connected to an input ofgate GFl.

Before describing the operation of the circuit arrangement in detail, it is important to appreciate several points of particular significant which enable the satisfactory functioning of the present circuit arrangements. It should be appreciated from the following description that the method of processor ar rangement checking, fault indication and processor identification is the so-called triplication method. However, instead of using additional processors for these purposes, which are in effect redundant apart from their checking function, spare time is utilized on the normal number of processors which are provided for the processing of data. For the letter method to be realized each processor must have the ability to deal with more processing than is actually required for the specific application. In the present case each processor is capable of processing more registers than are required. In addition, with respect to the two phases of operation in relation to the odd and even processors and the pulse TMl and TMZ related to this operation, the total period of these two pulses together must not exceed the shortest period between significant pulses of information contained within the input data, otherwise some of this data may be missed. Finally, the quantity of processing arrangements in association with fault-indication and processor arrangement identification circuits necessary for checking, fault-indicating and processor arrangement identification purposes will always be an even number but never less than four. This point will become clear from the following description of the operation of the circuit arrangement.

Consideration will now be given to the operation of the circuit arrangements in the first phase of operation It is assumed that all the bistable devices Tl/2, T2/3, T3/4 TN and T1, T2, T3 TN have been reset by the application ofa suitable pulse to the conductor designated GR, Now, upon the occurrence of pulse TM], each odd-numbered processor is caused to process its own associated register. Processor PROCl inputs to register REG! by way of gate GlB and this register returns an output to PROCl by way of gate (31C. Both gates G18 and 61C are primed by pulse TMI as is gate GlF which permits new input-data to enter processor PROCl by way of the lead designated l/Pl. Each remaining odd numbered processor processes its own associated odd-numbered register, by way of gates corresponding to gates GlB and 01C, the new input-data being presented to the gates corresponding to gate GlF. For instance, in the case of processor PROC3 its output is fed by way ofgate G38 to the input of register R563 and the output of this register is returned to the input of the processor by way of gate (33C. New input-data is presented to processor PROC3 by way of the lead designated UPS and gate G3F.

Each odd-numbered register also outputs into its immediately preceding even-numbered processor, for instance, in the case of registers REG] and REG3 to processors PROCN and PROCZ respectively by way of gates 01A and GJA respectively which are both primed by pulse TMl.

Similarly each of the remaining odd-numbered processors outputs into its immediately even-numbered preceding processor by way of gates corresponding to 01A and (33A. The output of each odd-numbered processor and its immediately preceding even-numbered processor are now compared. For in stance, the output from processor PROC3 is directed by way of gate 03D, which is primed by pulse TM], to one input of the comparator COMP2/3, whereas the output of processor PROC2 is fed by way of gate GZE, which is also primed by pulse TM], to the other input of the comparator COMPZ/J. Likewise, the output from processor PROCl is fed by way of gate GlD, which is primed by pulse TM], to one input ofcomparator COMPN/l, whereas the output of processor PROCN is fed by way of gate GNE, which is primed by pulse TMl, to the other input of comparator COMPN/l. The outputs from the remaining oddand evenmumbered processors are fed by way of gates corresponding to (BB together with GZE respec tively and gates GlD together with GNE respective to comparators corresponding to comparators COMP2/3 and COMPN/l respectively.

At this juncture it is important to appreciate that each processor, besides having the output of the immediately succeeding register presented to an input thereof, has in addition new input-data, that is presented directly to the immediately succeeding processor, also presented to it. For example, processor PROCl has input l/PZ gated with pulse TM2 at gate GlG, to present the same new input-data concurrently to processor PROC] as that presented to processor PROCZ, Likewise, processor PROC2 has input l/P3 gated with pulse TM] at gate GZG, to present the same new input-data concurrently to processor PROCZ as that presented to processor PROC3. Similarly each of the remaining processors PROC3 to PROCN has the same new input-data presented to it concurrently as that presented to the immediately succeeding processor, by way of gates corresponding to gates (HO and GIG. These particular arrangements ensure that if new input-data enters any processor, the immediately preceding processor is updated with this new input-data so that providing the processors, whose outputs are presently being compared, are functioning correctly, no disparity is indicated between the inputs of any of the appropriate comparators e.g. COMPl/Z, COMP2/3, COMP3/4, COMPN/l and so on.

Without the foregoing arrangement, disparity would occur between the inputs of the appropriate comparators when new input-data is presented to any processor since this new inputdata would not be presented to the immediately preceding processor until the data had been processed through the register associated with the processor receiving this new inputdata, and accordingly a delay in presentation of this new input-data to the immediately preceding processor would be encountered as a result of which differing processor outputs would be applied to the appropriate comparator.

If it is now considered that during normal processing procedure in the first phase of operation, one of the processors does not function correctly say, for example, processor PROCI, then since the output of this processor is being compared with the output of processor PROCN a disparity occurs between the two processor outputs and, therefore, also between the inputs of comparator COMPN/l which immediately gives a significant output that "sets bistable TN/l. As far as comparator COMPN/l is concerned this item of equipment only registers a disparity between the outputs of processors PROC] and PROCN, but is not able to identify which processor is at fault. Accordingly, the output of corn parator COMP/l primes gates GFN and GFl in preparation for the setting" ofeither bistable TN or T1 respectively in the second phase ofoperation of the circuit.

Upon the termination of pulse TMl, the first phase of operation of the circuit is complete and the second phase of operation of the circuit commences upon the occurrence of pulse TMZ. During the second phase of operation, each evennumbered processor processes its own associated register. For instance, processor PROC2 inputs to register REGZ by way of gate 028, which is primed by pulse TM2, and register REG] outputs into processor PROCZ by way of gate 02C, which is also primed by pulse TM2. Gate 02F is also primed by pulse TMZ and permits new input-data to enter processor PROCZ by way of the lead designated l/PZ. Likewise, processor PROCN outputs into register REGN by way of gate GNB, which is primed by pulse TMZ, and register REGN outputs into processor PROCN by way of gate GNC which is also primed by pulse TMZ. New input-data is presented to processor PROCN over the conductor designated l/PN and gate GNP which is primed by pulse TM2. Each remaining evennumbered processor processes its own associated even-numbered register by way of gates corresponding to gates GZB together with (32C and gates GNB together with GNC. New input-data to these remaining even-numbered processors is presented by way of gates corresponding to GZF and GNF.

Each even-numbered register also outputs into its immediately preceding odd-numbered processor, for instance in the case of registers REGZ and REGN to processors PROCl and PROC(NI) (not shown) respectively by way of gates 02A and GNA respectively, which are both primed by pulse TMZ. Similarly each of the remaining even-numbered processors outputs into its immediately preceding odd-numbered processor by way of gates corresponding to 62A and GNA. The output of each even-numbered processor and its immediately preceding odd-numbered processor are now compared. For instance, the output from processor PROCZ is directed by way of gate 02D, which is primed by pulse TM2, to one input of the comparator COMPl/Z, whereas the output of processor PROCl is fed by way of gate GlE, which is also primed by pulse TM2, to the other input of comparator COMPl/Z. Likewise, the output from processor PROCN is fed by way of gate GND, which is also primed by pulse TMZ, to one input of comparator COMP(Nl)/N (not shown), whereas the output of processor PROC(N--l) (not shown) is fed by way of gate G( N-l )E (not shown) to the other input of comparator COMP( N] )/N. The outputs from the remaining evenand odd-numbered processors are fed by way of gates corresponding to C20 together with GlE respectively and gates GND together with C(N-l )E (not shown) to comparators corresponding to comparators COMPl/Z and COMP( Nl )IN (not shown) respectively.

Each odd-numbered processor, besides having the output of the immediately succeeding even-numbered register fed to an input, has in addition new input-data that is fed to it and is also fed directly to the immediately succeeding even-numbered processorv For example, processor PROCl has input l/P2 gated with pulse TM2 at gate GIG to present the same new input-data to this processor as that presented to processor PROC2. Similarly, processor PROC(NI) (not shown) and the other remaining odd-numbered processors which are not shown, each have the same new input-data, that is fed to the respective immediately succeeding even-numbered processors, fed to them by way of gates corresponding to gate GIG. In the manner similar to the first phase of operation of the circuit, each processor being fed with data from the immediately succeeding register is ensured of being updated with the same new input-data which is being fed to the processor controlling the succeeding register. The reason for this particular arrangement is similar to that previously described in the first phase of operation of the circuit.

It will be recalled that during the first phase of operation it was considered that processor PROCl did not function correctly and because of this a disparity was registered between the outputs of processor PROCl and processor PROCN by comparator COMPN/l. The output of comparator COMPN/l ste" bistable TN]! and the set S output of this primed gates GF] and GFN in preparation for the opening of an appropriate one of these gates to set bistable T1 or TN in the second phase of operation according to which of processors PROCl and PROCN is not functioning correctly. Accordingly, because by the operation of bistable TN/l during the first phase of operation an indication is given that either processor PROCl or PROCN is not functioning correctly. in the second phase of operation a check is now made to determine exactly which of these processors is at fault. To determine this, the output of processor PROCN is compared with the output of processor PROC(N-l) (not shown) by comparator COMP(NI )[N (not shown) and the output of processor PROC] is compared with the output of processor PROC2 by comparator COMPl/Z. As previously processor PROCl was nominated as being faulty there will be a disparity between the outputs of processors PROC! and PROCZ, so comparator COMPIIZ will give a significant output which will set bistable and S output of this bistable now opens gate GFl, which has been previously primed from the setS output of bistable TN/l, and the output of gate GFl now sets" bistable Tl which duly gives a significant output on conductor F1 to identify which processor is at fault. The output on conductor F] can be used to actuate a fault printout and/or busying out of the faulty processor.

Faults occurring on other processors are detected and identified in a manner similar to thatjust described for processor PROCl ie. during the first phase of operation, each oddnumbered processor processes its own associated register and the output of each odd-numbered processor is compared with the output of its immediately preceding even-numbered processor, and then if a disparity occurs between any two out puts being compared, the bistable device associated with the comparator indicating the disparity is "set. Further, the output from this bistable primes two gates which are directly associated with two further bistable devices, either of which, when "set." identifies the faulty processor. However, neither of these bistables can set" until two further comparisons of the outputs of certain processors have been examined. These comparisons take place during the second phase of operation when each even-numbered processor processes its own associated register and the output of each even-numbered processor is compared with the output of its immediately preceding odd-numbered processor. A disparity now occurs between the faulty processor, of the two processors whose outputs were compared in the first phase of operation, and the processor whose output it is now compared with. As a result the appropriate one of the two gates previously primed is now opened and the further bistable corresponding to the faulty processor is "set" to give a significant output to identify the faulty processor. The application of a suitable pulse to conductor GR later, after the fault has been recorded and rectified, will reset" any bistable devices which have been det" during the operating sequence.

It will be appreciated by those skilled in the art that although each processor is shown associated with one register only, by judicious arrangement of the circuit a plurality of registers can time share one processor so that each register can in effect be processed in turn by that processor during the processing cycles i.e. during the first and second phases of operation. Say, for instance, that eight registers are provided for each processor, then the output from the relevant pr0ces sor is gated with either TM], for registers associated with oddnumbered processors, or with pulse TMZ, for registers as sociated with even-numbered processors, and also, to provide an input to each difierent register, with a different pulse of eight successive pulses of equal duration and in total duration equal to the duration of pulse TM] or TMZ. The individual outputs of the registers are gated similarly to the individual inputs and are combined in a single OR gate (when anyone significant input or more than one significant input is/are present on the gate at any one time a significant output is produced), the output of which is returned to the input of the associated processor.

Where more than one register is processed by a single processor, two phases of operation are employed, one phase for processing successively all the registers associated with odd-numbered processors and for making operational checks concurrently against the preceding even-numbered proces sors, and the other phase for processing successively all the registers associated with even-numbered processors and for making operational checks concurrently against the preceding odd-numbered processors. There is, however, an alternative method of operation which is to commence the sequence of operations by processing the first register associated with each odd-numbered processor, while operational checks are made concurrently against preceding even-numbered processors, and then to process the first register associated with each even-numbered processor, while operational checks are made concurrently against preceding odd-numbered processors. The sequence is continued, processing alternately a register associated with each odd-numbered processor, followed by processing a register associated with each even-numbered processor until all the registers have been processed and their associated processors checked for correct operation.

This alternative method does not necessitate any alteration in the circuit as shown, apart from the provision of suitable gating arrangements required for each processor to process eight registers each on a time-sharing basis, but does require the timing of the phase pulses to be changed. Accordingly, the frequency of pulses TM l and TM2 is increased and the duration of each pulse pulse is decreased such that each pulse is equal to the processing period of a register, in addition, because of the new phase pulse timing arrangements, instead of there being eight different successive pulses for register selection, 16 different successive pulses are provided. The operational sequence in this arrangement is then as illustrated in table I in which is represented to register selection pulses l to 16 and phase pulses TMl and TMZ. Although the phase pulses are shown in the table they are not utilized in the selection of the respective registers but it should be understood that during the occurrence of phase pulse TMl the registers associated with odd processors are processed, whereas during the occurrence of phase pulse TMZ the registers associated with even processors are processed. Each register selection pulse, when combined with the appropriate register output, in suitable gating arrangements, selects for processing the respective registers indicated in the body of the table Table l Registers selected for processing during the occurrence of phase For instance, register selecting pulse 1, during the occurrence of phase pulse TMl, selects register REGl/ODD for processing and this designation represents the first register in a group of registers associated with an odd-numbered processor, whereas register-selecting pulse 2, during the occurrence of phase pulse TM2, selects register REGl/EVEN for processing and this designation represents the first register in a group of registers associated with an even-numbered processor. Similarly, the registers designated REGZ/ODD to REGB/ODD in the table representing registers associated with an odd-numbered processor and the registers designated REGZ/EVEN to REGS/EVEN in the table representing registers associated with an evennumbered processor are each selected for processing purposes by an appropriate en of the register-selecting pulses and the relevant register output during the occurrence ofan appropriate one of the phase pulses.

The arrangements for processor checking and processor identification in the event of a fault arising are as already described, ie. during the occurrence of phase pulse TM] when registers associated with odd-numbered processors are being processed, an operational check is also made against the immediately preceding even-numbered processors to detect if any processor is not functioning correctly, and then upon the termination of phase pulse TMl, phase pulse TMZ occurs during which period the even-numbered processors are processed and an operational check is also made against the immediately preceding odd-numbered processors in order to identify the faulty processor, if such a processor is detected during the occurrence of phase pulse TMl.

Further alternative arrangements of operation involving either different pulse timing arrangements or different gating arrangements, or both these arrangements together will be apparent to those skilled in the art and therefore the present embodiment and is described alternative are not intended to limit the scope of the invention.

A further alternative to the specific circuit arrangements shown will be apparent to those skilled in the art, involving the advancement of data from the output of any register to the immediately succeeding processor, for checking purposes, in stead of the immediately preceding processor. Further modifications to the circuit arrangement that are required to put this alternative arrangement into effect are firstly, that gate circuits controlling the outputs from the processors to the comparator circuits presently having pulse TMl applied to them have pulse TMZ applied to them instead, whereas those gate circuits presently having pulse TMZ applied to them have pulse TMl applied to them instead. Secondly, the gate circuits such as G10, (32G, G36 and so on to gate GNG which presently control new input-data from the immediately suc ceeding processor are arranged to control new input-data from the immediately preceding processor. The circuit now operates in a manner substantially as that already described.

We claim:

I. In a data processing arrangement a checking and fault-indicating arrangement associated with an even number of processors, at least four, comprising a first group of processors, a second group of processors equal in number of said first group of processors, means effective during a first predetermined period for controlling each of the processors of said first group to perform a processing operation, means effective during said first predetermined period for applying the data applied for processing to a processor of said first group to a particular processor of said second group, means efiective during a second predetermined period for controlling each of the processors of said second group to perform a processing operation, means effective during said second predetermined period for applying the data applied for processing to a second processor of said second group to said processor of said first group, a first comparator individual to said processor of said first group and to said particular processor of said second group, means effective during said first predetermined period for applying the outputs of said processor of said first group and said particular processor of said second group to said first comparator, a second comparator individual to said processor of said first group and said second processor of said second group, means effective during said second predetermined period for applying the outputs of said processor of said first group and said second processor of said second group to said second comparator whereby a significant output is obtained from said first and said second comparators if said processor of said first group is faulty and an indicating arrangement to which the significant outputs of said first and second comparators are applied and which give an indication of the faulty processor.

2. A checking and fault-indicating arrangement as claimed in claim I. wherein the outputs of said second processor of said second group and a second processor of the first group are applied to a third comparator individual to said two processors during a predetermined period succeeding said second predetermined period and corresponding to said first predetermined period and if said second processor of said second group is faulty, and significant outputs of said second and third comparators applied to said indicating arrangement will identify the faulty processor.

3. A checking and fault-indicating arrangement as claimed in claim 1, wherein the processors are arranged in a ring formation and the first group' of processors are the odd-numbered processors in the ring and the second group are evennumbered processors, the data applied for processing to an odd-numbered processor during the first predetermined period being also applied to the immediately preceding evennumbered processor in the ring whereas the data applied for processing to the immediately succeeding even-numbered processor in the ring during the second predetermined period is also applied to said odd-numbered processor 4. A checking and fault-indicating arrangement as claimed in claim 3, wherein a shift register is associated with each one of the processors and gating arrangements are provided which enable the output of a shift register to be gated into the associated processor and into the immediately preceding processor in the ring during one of the predetermined periods 54 A checking and fault-indicating arrangement as claimed in claim 4. wherein gating arrangements are provided for updating during said first predetermined period the data applied to a processor from its associated shift register and for updat ing during said second predetermined period the data applied to said processor from the shift register associated with the immediate succeeding processor in the ring.

6. A checking and fault-indicating arrangement as claimed in claim I. wherein said indicating arrangement comprises two two-state switching devices for each comparator, the switching devices having set and reset sides and a significant output from a comparator sets the first of the associated switching devices, the set output of said first comparator and the set output of said second comparator being applied to an AND circuit. the output of which sets the second of the associated switching devices, the set output of which identifies the faulty processor. 

1. In a data processing arrangement a checking and faultindicating arrangement associated with an even number of processors, at least four, comprising a first group of processors, a second group of processors equal in number of said first group of processors, means effective during a first predetermined period for controlling each of the processors of said first group to perform a processing operation, means effective during said first predetermined period for applying the data applied for processing to a processor of said first group to a particular processor of said second group, means effective during a second predetermined period for controlling each of the processors of said second group to perform a processing operation, means effective during said second predetermined period for applying the data applied for processing to a second processor of said second group to said processor of said first group, a first comparator individual to said processor of said first group and to said particular processor of said second group, means effective during said first predetermined period for applying the outputs of said processor of said first group and said particular processor of said second group to said first comparator, a second comparator individual to said processor of said first group and said second processor of said second group, means effective during said second predetermined period for applying the outputs of said processor of said first group and said second processor of said second group to said second comparator whereby a significant output is obtAined from said first and said second comparators if said processor of said first group is faulty and an indicating arrangement to which the significant outputs of said first and second comparators are applied and which give an indication of the faulty processor.
 2. A checking and fault-indicating arrangement as claimed in claim 1, wherein the outputs of said second processor of said second group and a second processor of the first group are applied to a third comparator individual to said two processors during a predetermined period succeeding said second predetermined period and corresponding to said first predetermined period and if said second processor of said second group is faulty, and significant outputs of said second and third comparators applied to said indicating arrangement will identify the faulty processor.
 3. A checking and fault-indicating arrangement as claimed in claim 1, wherein the processors are arranged in a ring formation and the first group of processors are the odd-numbered processors in the ring and the second group are even-numbered processors, the data applied for processing to an odd-numbered processor during the first predetermined period being also applied to the immediately preceding even-numbered processor in the ring whereas the data applied for processing to the immediately succeeding even-numbered processor in the ring during the second predetermined period is also applied to said odd-numbered processor.
 4. A checking and fault-indicating arrangement as claimed in claim 3, wherein a shift register is associated with each one of the processors and gating arrangements are provided which enable the output of a shift register to be gated into the associated processor and into the immediately preceding processor in the ring during one of the predetermined periods.
 5. A checking and fault-indicating arrangement as claimed in claim 4, wherein gating arrangements are provided for updating during said first predetermined period the data applied to a processor from its associated shift register and for updating during said second predetermined period the data applied to said processor from the shift register associated with the immediate succeeding processor in the ring.
 6. A checking and fault-indicating arrangement as claimed in claim 1, wherein said indicating arrangement comprises two two-state switching devices for each comparator, the switching devices having set and reset sides and a significant output from a comparator sets the first of the associated switching devices, the set output of said first comparator and the set output of said second comparator being applied to an AND circuit, the output of which sets the second of the associated switching devices, the set output of which identifies the faulty processor. 